The massive grid failure in India last week affected more than 600 million people. Amidst speculation on the reasons for the failure, we decided to talk to engineers working at the load dispatch centers on the ground to get a firsthand understanding of what really happened.

Demand/Supply Mismatch: Even though demand/supply mismatch led to the grid failure, this is nothing new and didn’t just happen overnight. India has always struggled with power shortages. In this instance, the fragile safety mechanisms (relays) seemed to have failed under pressure from having to meet rising demand from the agricultural sector due to weak monsoons and mismanagement by regional dispatch centers.

This year’s monsoons have been weak and delayed in India, and the lack of precipitation is felt acutely in some northern states that are dependent on agriculture. The sowing of sugarcane has started in some states and there is high demand for power for irrigation. The state of affairs is politically very sensitive and there have been instances where the farming community has become extremely agitated during times of power shutdown. Moreover, no elected officials want to displease the farmers because of their political clout.

The Indian Grid: There are five major grids in India connecting the regions they are named after: Northern, Southern, Eastern, Western, and Northeastern. There is also a new grid interconnecting the Northern, Eastern, Northeastern, and Western grids called 'NEW.' It was the NEW grid that failed and through a cascading effect, the Northern, Northeastern and Eastern grids also failed. The Western grid isolated automatically and avoided the failure, whereas the Southern grid was unaffected because it is an asynchronous system (the Southern grid is connected in DC transmission by means of three HVDC links).

As a rule, all states in India are given a central government allocation from Central Generating Stations (National Thermal Power Corporation, National Hydroelectric Power Corporation and Nuclear Power Corporation of India Limited) to draw power from the National Grid, which comprises the nation’s five grids. This task is handled by the regional load dispatch centers that are responsible for managing the demand and supply of power to their respective regions in coordination with State Load Dispatch Centers (SLDCs).

In India, the power frequency of the grid is 50 cycles. If demand exceeds supply, the frequency drops. When there is a drop in frequency, adjustments have to be made by varying generation or shedding load (there is Automated Generation Control in the case of surplus generation). States will receive a first warning when the frequency of the grid falls below 49.7 cycles; a second warning goes out at 49.5 cycles.

It is important to note that the frequency of the NEW grid is different from the frequency of the Southern grid, as there are many more states connected to the NEW grid, putting it under significant pressure. Frequency fluctuations can be very high at any given time.

What Happened Last Week: Last week, two states allegedly overdrew power beyond their allocation while grid frequency was falling to dangerous levels. The NEW grid tripped and cascaded to the Northern and Eastern grids. The Western grid managed to survive by rapidly reducing demand and managing its existing supply and islanding from the NEW grid.

Why Did It Take So Long to Restore Power? A grid is an interconnected system of generation, transmission and load. During this grid failure, the generation tripped and had to be restored in phases and matched with the system. Also, the Northern grid is highly dependent on thermal power supply, i.e., coal. Hydropower generates a small percentage of power for the Northern grid, but the below-average precipitation from monsoon season has pushed that hydropower generation even lower. Once thermal power stations are shut off due to this kind of tripping, it normally takes at least six to eight hours to come back on-line because they have to be cooled and stabilized, whereas hydropower plants can come back on-line immediately. Because the Northern grid is largely dependent on coal and nuclear power plants, it takes much longer to restore when tripped.

Could This Historic Blackout Have Been Avoided? Yes. This was a clear case of mismanagement by the regional load dispatch centers which were negligent or did not see the warning signals. There should have been a safety mechanism that automatically shuts off load when frequencies drop down to dangerous levels due to the overdrawing of power. For example, the Southern grid has deployed an ‘Under Frequency (UF) Load’ mechanism which will not allow states to draw more power from the grid when the frequency dips below 49.5 cycles. There is also a System Protection Scheme (SPS) in the Southern grid where the load feeder in the grid systems will trip when there is a problem, allowing the main grid to remain safe and stable. Hence, such catastrophic grid failures are very rare in the Southern grid.

In fact, the Northern grid also has such systems in place (UF and SPS), but they generally are not implemented due to non-technical and political issues. Per the Indian Electricity Grid Code (IEGC), the area of responsibility on maintaining the grid is clearly defined on regional load dispatch instructions to be followed by SLDCs.

Supervisory control and data acquisition (SCADA) systems help in providing facts and detecting problems on-line and in real time; however, managers still have to act on these facts, which creates the potential for human error. In India, increasing power supply and transmission capacity are critically important issues. However, the blackouts of 2012 have made it abundantly clear that there is also a critical need to put automated safety mechanisms in place across the country to avoid such catastrophes in the future.